1. Field of the Invention
The present invention relates to a system and method for processing substrates. Specifically, the invention relates to a system and method having a thermally conductive and electrically insulative member to dissipate heat in a substrate processing chamber.
2. Background of the Related Art
Sub-quarter micron multi-level metallization represents one of the key technologies for the next generation of ultra large scale integration (ULSI) for integrated circuits (ICs). As circuit densities increase, the widths of vias, contacts and other features decrease to 0.25 xcexcm or less, while the thicknesses of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling structures where the aspect ratio exceeds 4:1, and particularly where it approaches 10:1.
To obtain deposition in the high aspect ratio features, one method uses a high pressure physical vapor deposition (PVD) process known as an ionized metal plasma (IMP) process. Generally, IMP processing offers the benefit of highly directional deposition with good bottom coverage on high aspect ratio structures. FIG. 1 is a schematic of a typical IMP chamber 10, having a coil 22 supported by a support 30 in the chamber 10. Typically, processing gas, such as helium or argon, is injected into the chamber and a power supply 12 delivers a bias to a target 14 to generate a plasma 13 of processing gas ions between the target and a substrate support 16, that supports a substrate 18. The ions impact the target and sputter material from the target, where some of the material is directed toward the substrate. A second power supply 20 delivers power to a coil 22 that is disposed between the target 14 and the substrate 18. The coil increases the density of the plasma and ionizes the sputtered material that traverses through the magnetic fields generated by the coil and the intensified plasma. A third power supply 24 biases the substrate and attracts the sputtered material ions in a highly directionalized manner to the surface of the substrate to better fill high aspect ratio features in the substrate. A clamp ring 26 is circumferentially disposed about the substrate to retain the substrate in position. A shield 28 is disposed between the chamber sidewalls and the sputtered material to avoid deposition of the sputtered material on the chamber sidewalls. Because the shield 28 is conductive, typically made of aluminum, and grounded and the coil 22 is conductive and electrically powered, electrical insulation between the two components is typically desired with an electrically insulative support 30.
FIG. 2 shows details of the typical support 30 of FIG. 1. The coil 22 is attached to the shield 28 by the combination of an internally threaded pin 36 at the coil coupled with a screw 34 near the shield having external threads 32. Because the coil is also sputtered by the plasma ions during the process, the coil is generally made from the same material as the target, e.g., copper. The pin and screw are insulated from the shield by an insulative support labyrinth 40, typically made of aluminum oxide (alumina). The alumina labyrinth is both electrically and thermally insulative. An inner cup 42 is placed between the coil and the support labyrinth to protect the inner surfaces of the support 30 from the sputtered material in proximity to the support. Because the inner cup is exposed to the plasma ions, generally the inner cup is also made from the same material as the coil. An outer cup 44, attached to the shield by bolts 46a, 46b, circumferentially encloses a portion of the inner cup to reduce sputtered material deposition on the inner surfaces of the support 30 and is generally made of conductive material, such as stainless steel. The assembly of the inner cup, support labyrinth, and outer cup between the shield and the coil are held in position by the screw 34 and pin 36. An insulative ceramic cap 48 protects and insulates the screw 34 from the chamber surfaces.
It has been discovered that heat buildup in the chamber, and particularly in the coil which is energized with power to generate the plasma, can have disadvantageous effects on the substrate process and resulting films. The heat can cause the structural components, such as the coil, to be distorted in shape, thereby altering the plasma density and shape. An increase in temperature can also cause the sputtering rates to change with varying coil temperatures. Increased temperatures can also limit the amount of power which can be applied to the coil without causing overheating of the coil. It is known that heat can be dissipated through conductive elements attached to a heat sink. However, typical conductive materials that channel heat to a heat sink are also electrically conductive which would disadvantageously affect the ability of the coil or other insulated electrical components to function properly.
Furthermore, the heat dissipation is hindered under vacuum conditions by the typical attachment, such as bolting or clamping, of the structural components. Under vacuum conditions, there are few molecules to transfer heat between adjacent surfaces. Even polished surfaces under magnification show irregularities in the surface. By bolting or clamping two surfaces together, the heat transfer across the interface between the surfaces is limited to the direct contact of the microscopic surfaces and hindered by the absence of interspaced molecules under vacuum conditions between the non-contacting portions of the two surfaces. Typically, greater numbers of interfaces causes an increased resistance to conduction. The typical support 30 has several interfaces and thus interferes with heat transfer.
Therefore, there remains a need to increase the thermal conductance between a chamber component, such as a coil, and a heat sink to allow the thermal loads to be dissipated more readily and yet still provide electrical insulation for the chamber component, especially under vacuum conditions.
The present invention generally provides a substrate processing system having a thermally conductive and electrically insulative member coupled to a heated member that provides for heat dissipation from the heated member. In a preferred embodiment, the present invention provides for heat dissipation through thermal conductance of an electrically insulated coil in an IMP reaction chamber.
In one aspect, the invention provides a system for processing a substrate, comprising a chamber, an electrically conductive member, and a thermally conductive and electrically insulative support supporting the electrically conductive member comprising a component having a thermal conductance value of at least 90 watts per meter-degree Kelvin (W/m-K) and an dielectric strength value as an indicator of electrical resistivity of at least 1014 kilovolts/millimeter (kV/mm). In another aspect, the invention provides a system for processing a substrate, comprising a chamber, an electrically conductive member in proximity to the chamber, and a thermally conductive and electrically insulative support supporting the electrically conductive member, the support comprising a component selected from the group consisting essentially of aluminum nitride and beryllium oxide. In another aspect, the invention provides a support for a substrate processing system comprising a ceramic and a metal conductor bonded to the ceramic. The invention also includes a method of cooling a substrate processing chamber, comprising providing a chamber, supporting an electrically conductive member in the chamber with a thermally conductive and electrically insulative bonded support, and providing at least one heat flow path from the electrically conductive member to the chamber through one or more bonded connections of the support. In another aspect, the invention provides a support for a substrate processing system, comprising a semi-conductor ceramic having a thermal conductance value of at least 90 W/m-K and a dielectric strength value of at least 1014 kV/mm. In yet another aspect, the invention provides a support for a substrate processing system, comprising a semi-conductor ceramic selected from the group consisting essentially of aluminum nitride and beryllium oxide.